In a bowl, combine pork, lemon juice, soy sauce, onions, garlic and pepper. Massage marinade into meat and marinate for about 30 minutes. Remove meat, onions and garlic from marinade, squeezing and reserving excess liquid.
In a pan over high heat, heat 2 tablespoons of the oil. Add pork and cook for about 3 to 5 minutes per side or until lightly browned. Spoon out and reserve released meat juices during frying. Remove meat.
In the pan, add the remaining 1 tablespoon oil. Add onions and garlic, and cook, stirring regularly, until limp and aromatic. Return meat to pan.
Add reserved marinade and meat juices. Add water and bring to a boil. Cover, lower heat and simmer for about 40 to 50 minutes or until meat is fork-tender and liquid is reduced. Season with salt to taste. Turn off heat and add the remaining onion rings. Cover and allow onion slices to cook slightly in the steam. Serve hot.